Annular tool

ABSTRACT

The invention relates to an annular tool ( 1 ) having at least one working region ( 4 ) oriented radially outward and having high wear resistance, and a clamping part ( 5 ) closer to the axis, in particular a roller bit or cutting ring for rock, in particular for tunnel boring machines, made of a material which is formed from an iron-based alloy as matrix having incorporated hard material particles, wherein the hard material particles are formed from carbide and/or nitride and/or oxide and/or boride, possibly as carbonitride or oxycarbonitride having a boron component of at least one of the elements, or in mixed form of the elements from groups 4 and 5 of the periodic system, and have a density at room temperature of more than 7400 kg/m 3 , preferably of more than 7600 kg/m 3 . The invention further relates to methods for the production thereof.

The invention relates to an annular tool having at least one workingregion oriented radially outward with high wear resistance and aclamping part closer to the axis, in particular a roller bit or cuttingring for rock, in particular for tunnel boring machines.

Furthermore, the invention relates to a method for producing annulartools having at least one working region oriented radially outward and aclamping part closer to the axis, in particular roller bits or cuttingrings for rock, in particular for tunnel boring machines, formed from aniron-based alloy as a matrix in which hard material particles, such ascarbides and/or nitrides and/or carbonitrides and/or borides, possiblyin mixed form of the elements from groups 4 and/or 5 of the periodicsystem, are incorporated.

PRIOR ART

Boring devices for rock formations or bedrock and the like are, forlarger diameters, typically equipped with annular tools which comprise aworking region oriented radially outward and which roll off of the rockbase under pressure and thereby cause a removal or breaking-away of therock base.

Tunnel boring machines, for example, have a large disk-shaped toolholder in which a plurality of what are referred to as roller bits orcutting rings are installed in a rotatable position. When drivenforward, the tool holder is rotated and pressed against the rock with ahigh force, wherein the roller bits arranged at different radii of thetool holder have a breaking effect in the respective regions of the rockand wherein the removed rock, or what is referred to as the chippings,is transported away behind the tool holder.

In accordance with the mechanical requirements, the annular tool with atapered working region oriented radially outward is to have in thisregion high wear resistance as well as high hardness and high toughnessof the material.

In most cases, the tool blank is shrink-fitted onto an axle, whereintensile stresses are inevitably produced in the clamping region, whichforces are, in the heavy operation breaking the hard rock, respectivelyoverlapped the compression stresses on the material necessary for theoperation and do not produce any essentially stationary stresses on thetool material.

Roller bits are thus to comprise a working region with the highestpossible wear resistance and a clamping region with sufficiently highhardness and high toughness and are to have overall superior breakageprotection of the material under alternating mechanical stress, since afailure of a tool causes costly repair work with downtime of the boringmachine.

The cutting rings are normally composed of a tool steel. The shapinggenerally occurs via a forging process, wherein the desired materialproperties are achieved by a subsequent heat treatment. It is known tothe ordinarily skilled artisan that, for tool steels, a highest possiblewear resistance can only be achieved with a high hardness of thestructure. Here, it must be assumed that the toughness of the structuredecreases as the hardness increases. To achieve the best properties fortool steels with respect to the harsh use as a cutting ring, acompromise must be made between superior wear resistance and hightoughness.

Various attempts were made to extend the service life of the cuttingrings by combining extremely wear-resistant materials with hard buttough materials. DE 10 2005 039 036 B3, for example, describes a rollerbit made of steel that comprises welded-on segments in the workingregion, wherein these segments contain hard metal particles of tungstencarbide. From JP 2000001733 A, a similar cutting ring is known which hasa hard metal ring attached to a base body of nodular cast iron at theouter circumference. Furthermore, from the documents JP 2007138437 A, GB1188305, GB 1379151, DE10300624A1 and DE 101 61 825 A1, cutting ringsfor tunnel boring machines are known which have segments or cylindricaland other specially formed parts made of hard metal arranged at theouter circumference which are connected to the base body by soldering,compression or molding. CA 2 512 737 A1 also describes a cutting ring inwhich segments of hard metal are axially clamped between two disks. Allof these known attempted solutions involve either very costly anddifficult production or result in the premature failure of the cuttingring during use, for example, due to high thermal stresses during use ordue to the softening of the solder. In JP 59144568 A, a productionmethod for cutting rings is described in which a melt that containstungsten carbide-based hard metal particles is cast into a rotatingmold, whereupon the hard metal particles are concentrated in the outerregion of the cast body. This method has the disadvantage that the hardmetal particles added to the melt are partially dissolved by the meltand that undesired, brittle structural components can form in thestructure of the tool during the solidification. The minimum size of theadded hard metal particles is also limited by the dissolution process.

OBJECT OF THE INVENTION

The object of the invention is to create a generic annular tool thatenables an increased service life during harsh, bedrock-breakingoperation.

It is also the object of the invention to specify a method of the typenamed at the outset for producing annular tools which, according to therespective demands, have an optimal material structure.

The aforementioned object of creating a generic annular tool thatenables an increased service life during harsh, bedrock-breakingoperation is achieved in that the tool is composed of a material whichis formed from an iron-based matrix alloy with hard material particlesincorporated therein. The hard material particles can thereby be formedfrom carbide, nitride, oxide or boride or as compounds thereof, such ascarbonitride, carboboride or oxycarbonitride with a boron component.Depending on the case of application, it can be advantageous thatmixtures of these different types of hard materials are contained in thetool. The metal component in the hard material particles comes primarilyfrom groups 4 and 5 of the periodic system (Ti, Zr, Hf, V, Nb, Ta),wherein here, too, only individual elements from these groups, ormixtures thereof, can be contained in the hard materials. Unlike thehard materials often used in iron metallurgy, whose metallic componentsstem from group 6 of the periodic system (for example, tungstencarbide), hard materials of metals from groups 4 and 5 have theadvantage that they exhibit only a slight solubility in an iron basemelt at the melting and casting temperatures of iron-based alloys of upto 1650° C. commonly found in practice.

It is known that hard materials which are formed or precipitated duringthe solidification of an iron base melt and during the subsequentcooling of the resulting workpiece preferably form eutectic crystallinestructures or are precipitated at grain boundaries. The hard materialsformed in such a manner can significantly reduce the toughness of thestructure. The advantage of the low solubility of the above hardmaterials in an iron base melt is then that, on the one hand, largequantities of these hard materials can be contained as solid particlesin the melt, whereas on the other hand, only small amounts of additionalhard material particles are formed or precipitated in the structureduring the solidification of the melt and during the subsequent coolingof the workpiece. These small amounts of brittle hard materials haveonly a slight negative influence on the toughness of the structure.These can even increase the toughness, however, if the precipitatedparticles are fine enough to reduce a grain growth of the matrix duringa heat treatment.

In order to achieve a high wear resistance and long service life of theroller bits, a minimum amount of hard material particles is to bepresent in the structure and the hard material particles are also to bedistributed in the cutting ring in such an inhomogeneous manner that ahigh proportion thereof is located in the working region of the rollerbit, which region is oriented radially outward. For what is considered asufficient volume fraction of the wear-resistant working region ofapproximately 8 percent by volume (vol. %), a hard material content ofat least 5 vol. %, based respectively on the entire workpiece, hasproven to be suitable. At least 8 vol. % of hard material particles isnecessary if harsh working conditions are intended for the cutting ring.The possible service life of the roller bit can be increased with alarger volume fraction of the working region. For example, theproportion of the working region can be increased up to approximately 25vol. % and higher in order to enable long service life undersimultaneously difficult conditions of use.

The desired distribution of the hard material particles in the cuttingring is achieved when the density thereof is higher than the density ofthe melt, and if the particles thus move outward in the centrifugalcasting process. Tests have shown that good results are already achievedwhen the density of the hard material particles at room temperature isgreater than 7400 kg/m³. A desired high concentration of the hardmaterial particles is achieved when the particles have a density greaterthan 7600 kg/m³ at room temperature. Hard materials with this densityare, for example, carbides, nitrides and carbonitrides of niobium, whichhave proven effective in tests. It has also been shown that a smalladdition of vanadium to these niobium hard materials can advantageouslyinfluence the growth and the properties of the particles, but that thedensity of the particles decreases with the addition of vanadium. Aratio of Nb atom %/V atom %>5 for niobium-vanadium mixed carbides, whichcan also possibly be carbonitrides, should be maintained in any case.Higher concentrations of these particles in the working region areachieved with a ratio of Nb atom %/V atom %>10.

It is known to the ordinarily skilled artisan that the wear resistanceof a structure is not only dependent on the hardness of the matrix andof the incorporated hard material particles, as well as on theproportions thereof, but also on the size distribution of the hardmaterial particles. All structural components that are not the hardmaterial particles referred to above are to be understood below asmeaning the matrix. If the hard material particles are too small, thenthey can be stripped from the matrix as whole particles during groovingwear without notably increasing the wear resistance. However, if theparticles are too large, they can fracture under the high compressiveload while being used to break bedrock and thus also cannot adequatelyincrease the wear resistance. In the present case of the roller bits, ithas been shown that superior results can be achieved if at least 60 vol.%, preferably at least 75 vol. %, of the hard material particles areformed with a size of less than 70 μm.

In addition to the properties of the hard material particles, theproperties of the matrix are also of critical importance in order toachieve high wear resistance in the working region of the roller bits.In particular, the properties of the matrix are critical in order toenable a sufficient toughness of the structure both in the workingregion and also in the clamping region. The properties of the matrix areprimarily determined by the chemical composition thereof and by apossible heat treatment. Carbon is the most important alloy element andinfluences above all the hardenability of the steel, whereinapproximately 0.28% C is considered the lower limit for a sufficienthardenability of the steel for the present purpose of use. With a carboncontent of over 1.2% in the matrix, a carbide network can form in thestructure, which network reduces the toughness of the same. Siliconincreases the strength and the wear resistance, as well as thecastability of the melt, but should not exceed 2% in the matrix.Manganese decreases the critical cooling rate for the formation of themartensite and, at a sufficient quantity of up to 2%, enables an airhardening of the cutting rings. By means of higher manganese contents ofup to 25%, the solubility of carbon in the austenite can besignificantly increased and the transformation properties of theaustenite during cooling or mechanical loading can be influenced. Withmanganese contents of up to 25%, the carbon amounts in the matrix canalso be up to 2.3%. Similar to manganese, chromium also increases thehardenability of the steel and forms secondary and tertiary carbideswhich are precipitated out of the austenite and increase the wearresistance, wherein excessively high chromium contents lead to achromium carbide network in the structure. The chromium content shouldtherefore not be higher than 6.0%. Like manganese and chromium, nickelalso facilitates the martensite formation and additionally increases thetoughness of the matrix. For nickel, a content of 2.5% as an upper limitin the matrix appears to be sufficient for achieving the necessaryproperties. For setting a low critical cooling rate, a combination ofMn, Cr and Ni has proven effective. At up to 2.2%, molybdenum increasesthe strength of the matrix and, through the formation of carbides,increases the wear resistance. In combination with Nb and V, tungstenforms mixed carbides and mixed nitrides and can thus increase thedensity of these hard materials. However, the content of W in the meltis to be set such that, after the centrifuging out of the hard materialsprimarily formed in the matrix, only a content of max. 1.5% is stillcontained, since together with Mo a network of W-Mo mixed carbides canotherwise be produced. For this reason, 1.5×Mo+W is also not to be morethan 3.5%. Due to the high affinity of Nb and V for C or N, only slightamounts of less than max. 0.8% thereof remain in the matrix.

Similar to Nb and V, only slight amounts of Ti, Zr, Hf and Ta alsoremain in the matrix. To increase the high temperature strength forcutting rings subjected to particularly high loads, cobalt can becontained in the matrix up to a content of 3%. For the purpose ofdeoxidation, Al is often added to the melt and can still remainpartially dissolved in the matrix after the solidification. By means ofhigher contents of Al, the density of the melt can be reduced and thedensity difference from the hard material particles thus increased. AnAl amount of up to 3% in the matrix is possible.

The alloys of the alloyed tool steels as they are described in the DIN10020 standard are particularly well suited as a base composition forthe matrix. Cold work steels, hot work steels and high-speed steels canbe used as a base composition for the matrix. To avoid eutecticcarbides, it is, in the case of high-speed steels, sometimes necessaryto reduce the carbon content compared to the standard composition. Withthese matrix alloys, the hardness of at least 44 HRC that is necessaryfor a trouble-free use of the cutting rings can be achieved by asuitable heat treatment, which is generally composed of a hardeningprocess and an annealing process. It has been shown that particularlygood wear resistance is achieved when the matrix of the cutting ringshas a hardness of 50 HRC and higher. This hardness is required whereboring takes place in hard, particularly abrading rock formations. Theheat treatment of the cutting rings must always be adapted to thespecific case of use of the application in order to achieve a balancedrelationship between the hardness and toughness of the structure.

If the matrix composition is selected such that it corresponds to anaustenitic manganese steel, then the advantage of a particularly toughand impact-resistant base structure can be utilized together with asurface which hardens under pressure and is thus wear resistant.‘Houdremont, Handbuch der Sonderstahlkunde, Springer Verlag, 1956’ andother literature sources describe austenitic manganese steels of thistype, which are also named Hadfield steels after their inventor and,according to their structure, are austenitic manganese tool steels.These steels have a manganese content of approximately 8 wt. % to 15 wt.%, in exceptional cases 6 to 25 wt. %, and a carbon content ofapproximately 0.8 to 2.3 wt. %. The ratio of wt. % of Mn to wt. % of Cis roughly 10:1. Austenitic manganese steels are, after a correspondingheat treatment, characterized in that their structure is composed of ametastable, extremely tough austenite. By applying pressure to thesurface, the metastable austenite can transform into a hard andwear-resistant martensite, whereby a part with a hard surface and atough core is obtained. The transformation behavior can be influenceddepending on the amount of Mn and C in the steel and the proportionthereof to one another.

To form the hard martensitic surface, the load during use may besufficient on its own. If the compressive load during use is not enoughto induce the required transformation of the structure in the region ofthe surface, then the surface region that is to be hardened can alreadybe hardened prior to use, for example, by hammering or a differentmechanical treatment. The composition of the matrix alloy can also beset such that the surface or the entire tool body can be transformed atleast partially into martensite by a cooling below room temperature,preferably by means of liquid nitrogen.

Roller bits described above or similar annular tools which contain atleast one working region oriented radially outward and a clamping partcloser to the axis and are composed of an iron-based alloy as a matrix,in which hard material particles, such as carbides and/or nitridesand/or carbonitrides and/or borides, possibly in mixed form of theelements from groups 4 and/or 5 of the periodic system, areincorporated, can be produced in that, in a first step, a base alloy ismelted, for example in an induction furnace, and heated to a temperatureof 1350° C. to 1630° C. This base melt is used to introduce most of thealloy elements into the melt for the subsequent finished alloy.

The base melt can, depending on the desired matrix composition anddepending on the selection of the design of the second step subsequentthereto, have the following composition by wt. %:

Carbon (C) up to 2.5

Silicon (Si) 0.01 to 3.0

Manganese (Mn) 0.05 to 28.0

Chromium (Cr) up to 9.0

Nickel (Ni) up to 4.3

Molybdenum (Mo) up to 3.5

Tungsten (W) up to 2.2

(1.5×Mo+W) up to 5.1

Vanadium (V) up to 6.0

Niobium (Nb) up to 35.0

Aluminum (Al) up to 3.5,

possibly

Titanium (Ti) up to 2.0

Zirconium (Zr) up to 3.0

Hafnium (Hf) up to 1.0

Tantalum (Ta) up to 5.0

Cobalt (Co) up to 3.5

Iron (Fe) and impurity elements as the remainder.

If the metallic components of the hard material particles that aresubsequently to be formed (elements from groups 4 and 5) are alreadycontained in the base melt, and if the content of C, N and B is at thesame time kept as low as possible, then carbon and/or nitrogen and/orboron are introduced into the base melt in a second step, whereuponthese elements combine with the elements from group 4 and/or 5 of theperiodic system, which are already present in the base melt, to formhard material particles that have a higher density than the melt. Thehard materials formed have the structure M_(x)(C+N+B)_(y), wherein thetotal proportion of carbon, nitrogen and boron in the hard materialsformed is between the atomic ratios 0.4 and 0.55, or the ratio x:y isbetween 1.5 and 0.8. The amount of alloyed carbon is to be chosen suchthat a carbon content of 0.3 to 2.3 wt. % C remains in the residualmelt. There is thus sufficient carbon available for forming martensitein the matrix during the subsequent heat treatment. The amount of theother alloy elements, except for those from the fourth and fifth groups,is based on the desired properties of the matrix surrounding the hardmaterial particles, wherein the formation of a eutectic carbide networkis to be avoided in order to achieve a highest possible toughness. Here,particular attention must be paid to the heat treatment properties ofthe matrix.

If the temperature of the base melt is kept between 1550° C. and 1630°C., there results a rapid formation of the hard materials simultaneouslywith low wear on the melting vessel. The alloying of carbon, nitrogenand boron can occur by means of solid materials, such as for examplecoke, ferrochrome with a high carbon content, silicon carbide,ferronitrogen and ferroboron, or by the addition of melts or gasescontaining carbon and/or nitrogen and/or boron. This component or thesecomponents can also contain other alloy elements. Depending on thecarbon, nitrogen and boron content of the added component(s), very largeamounts thereof can be necessary in order to achieve the desired carbon,nitrogen and boron content in the final melt. The amount of the addedcarbon, nitrogen and boron carriers can thus also be significantlylarger than the amount of the base melt, which means that the alloyelement components in the base melt can take on very large contents, forexample, up to 35 wt. % of niobium.

The melting of an alloy rich in the elements from the fourth and/orfifth main group with small contents of carbon, nitrogen and boron hasthe advantage that the ferroalloys, via which the elements from thefourth and fifth groups are generally alloyed, liquefy quickly. If thecarbon, nitrogen and boron contents in the melt are too high, a hardmaterial layer can form on the surface of the ferroalloy pieces used,which layer markedly impedes the liquefaction. It has been shown intests that the proportion of carbon in the base melt is to be less than0.6 wt. % in the above case.

It is also possible to set the composition of the base melt in the firststep such that the melt does not contain the elements for forming thehard material particles and that, in the second step, the hard materialparticles are added by means of a solid or liquid metallic premelt, orby means of a similar mixture of metal and hard material particles, andare distributed homogeneously in the base melt. These hard materialparticles can be carbides and/or nitrides and/or oxycarbonitrides and/orborides, possibly as carbonitrides and/or oxycarbonitrides with boroncomponents, at least of one of the elements, or in mixed form of theelements, of groups 4 and 5 of the periodic system. The homogeneousdistribution of the hard material particles in the base melt can befacilitated by mechanical processes, for example by stirring, or byblowing in gases in the lower region of the melting vessel.

Depending on the melt composition and the composition of the formed orintroduced hard material particles, it can be advantageous, for examplein order to prevent an oxidation of components in the melt, to performprocess steps 1 and/or 2 completely or merely partially under an inertgas atmosphere or under reduced ambient pressure.

Following the homogeneous distribution of the hard metal particles inthe second step, the matrix melt with the hard material particlescontained therein is, in a third step, cast into a rotating mold andallowed to solidify. Produced by the rotational motion about thelongitudinal axis of the mold and the centrifugal force acting on themelt and the hard material particles as a result, the hard materialparticles migrate outwards into the eventual working region of theroller bit, where a crystalline structure highly rich in hard materialsforms. At the same time, a crystalline structure forms in the interiorregion, which structure has only small contents of the primarilyprecipitated or introduced hard materials. The resulting amount of hardmaterials in the outer region is mainly determined by the processparameters of rotational speed of the mold, the density differencebetween the hard material particles and the melt, the size distributionof the hard material particles, and the cooling rate of the melt in therotating mold. In order to achieve a high concentration of hard materialparticles in the outer region and thus high wear resistance, therotational speed of the mold and therefore the centrifugal accelerationacting on the melt and on the hard material particles should be as highas possible. Centrifugal accelerations of 700 m/s² and higher, measuredat the outer diameter of the cast piece, have proven effective. A largedensity difference between the hard material particles and the melt canmainly be achieved with high proportions of niobium, tantalum andhafnium in the hard materials. For cost reasons, hard materialsparticularly rich in niobium, specifically niobium-vanadium mixedcarbides, have proven advantageous for achieving a high hard materialcontent. The hard material particles precipitated or added in the secondstep are in any case to have a density that is greater than that of thematrix melt at a temperature 50° C. above the liquidus temperature.

The migration of the hard material particles outward requires adifferent length of time depending on the dimensions of the cast piece,and in order to achieve a maximum possible concentration of hardmaterials in the outer structure, the duration between the time at whichthe melt is cast into the mold and the solidification of the melt shouldbe as long as possible. Here, preheating the mold to several 100° C. canprovide small advantages. The solidification rate can be reduced to aparticularly significant extent if the mold is composed, wholly or inparts that face the cast piece, of a material that exhibits only verypoor thermal conductivity. Here, quartz sand and molding materials withan aluminum-silicate-ceramic base should be mentioned. A ceramic- orcarbon-based heat-insulating coating on the inner side of the moldprovides advantages in this case.

After the blank has been cast, it can, in order to keep stresses in thering low, be removed from the mold at a temperature of up to 1000° C.,the temperature can be equalized across the entire ring in a furnace,and the blank can then be slowly cooled such that the matrix structureis present in a soft state at room temperature. Here, the cooling rateis based on the alloy composition of the matrix. If necessitated by thesubsequent conditions of use of the roller bit, for example boring intoparticularly hard rock, then after the blank is emptied from the mold,it can be brought to the proper forging temperature in a furnace and canthen be plastically deformed in one or more steps in a drop forgingprocess. By means of this process, the toughness of the structure can besignificantly increased. The forging process is then followed by thecontrolled cooling to room temperature. The blank can then bemechanically preworked, for example by turning, whereupon a heattreatment of the ring follows. The heat treatment can, in the case of amatrix composition similar to a tool steel, be composed of a hardeningprocess and at least one annealing process. For a matrix compositionsimilar to an austenitic manganese steel, a rapid cooling generallyoccurs after an annealing in order to achieve a metastable austeniticstructure. After the heat treatment, the mechanical final working of thecutting ring occurs, for example by turning and/or grinding.

The invention is described below with the aid of an executed example.

A premelt with 0.28% C, 1.3% Si, 0.9% Mn, 1.34% Cr, 2.2% Ni, 0.1% Mo,0.8% V and 10.0% Nb was melted in an induction furnace, brought to atemperature of 1590° C., held at this temperature for 5 minutes andthen, at a constant temperature, brought to a carbon content of 2.35%using petroleum coke. After the carburization, the final melt wasreduced to a temperature of 1570° C., kept there for 3 minutes andsubsequently cast in a centrifugal casting process. A steel mold wasused as a centrifugal casting mold, into which a core of bound silicondioxide was inserted. This core had previously been coated on the innersurface with a 1-mm thick zirconium oxide-based layer. The cast piecewas removed from the mold at approximately 800° C. and, after anequalization phase of 60 minutes in the furnace, cooled to roomtemperature in the furnace, after which it was preworked and brought toa hardness of 53 HRC in the clamping region by means of a hardening anddouble annealing.

FIG. 1 shows, by way of example, a cut-open annular roller bit 1 withthe cross section 2. The part 3, which is enriched with hard materialparticles, comprises the working region 4 positioned at the outerdiameter of the ring 1. The clamping region 5 is positioned at the innerdiameter of the ring 1 and contains only a low proportion of hardmaterials.

FIG. 2 shows, by way of example, the structure in the working region 4,wherein the hard material particles are shown in a light depiction andthe matrix is shown in a dark depiction. The hard material content isapproximately 20%.

FIG. 3 shows, by way of comparison, the structure in the clamping region5 with only a low proportion of hard materials.

1. Annular tool (1) having at least one working region (4) orientedradially outward with high wear resistance and a clamping part (5)closer to the axis, in particular a roller bit or cutting ring for rock,in particular for tunnel boring machines, characterized in that the toolis composed of a material that is formed from an iron-based alloy as amatrix with incorporated hard material particles, wherein the hardmaterial particles are formed from carbide and/or nitride and/or oxideand/or boride, possibly as carbonitrides or oxycarbonitride with a boroncomponent, at least of one of the elements, or in mixed form of theelements, from groups 4 and 5 of the periodic system, and have a densityat room temperature of greater than 7400 kg/m3, preferably of greaterthan 7600 kg/m3.
 2. Tool (1) according to claim 1, characterized in thatthe hard material particles are present in the tool to an extent of atleast 5 vol. %, in particular of more than 8 vol. %, wherein the hardmaterial particles are inhomogeneously distributed across the toolcross-section (2) and have a higher volume fraction in the workingregion (4).
 3. Tool (1) according to claim 1, characterized in that theworking region (4) has a volume fraction of at least 8.0%, preferably ofat least 14.0%, in particular of approximately 20% to 25%, of the tool(1), in which working region more than 60 vol. %, preferably more than75 vol. %, of the hard material particles are formed with a size of lessthan 70 μm.
 4. Tool (1) according to claim 1, characterized in that thehard material particles are essentially formed as niobium-vanadium mixedcarbides, possibly with a nitrogen component, and that they have a ratioof atom % of Nb to atom % of V of greater than 5, preferably greaterthan 10.Nb [atom %]/V [atom %]>5, preferably>10
 5. Tool (1) according to claim1, characterized in that the matrix alloy has a chemical composition bywt.% within the limits of Carbon (C) 0.28 to 2.3 Silicon (Si) 0.01 to2.0 Manganese (Mn) 0.05 to 25.0 Chromium (Cr) up to 6.0 Nickel (Ni) upto 2.5 Molybdenum (Mo) up to 2.2 Tungsten (W) up to 1.5 (1.5×Mo+W) up to3.5 Vanadium (V) up to 0.8 Niobium (Nb) up to 0.4 Cobalt up to 3.0Aluminum (Al) up to 3.0, possibly Titanium (Ti) up to 0.2 Zirconium (Zr)up to 0.2 Hafnium (Hf) up to 0.1 Tantalum (Ta) up to 0.25 Iron (Fe) andimpurity elements as the remainder.
 6. Tool (1) according to claim 5,characterized in that the matrix alloy is composed of tool steel with ahardness of greater than 44 HRC, preferably of 50 HRC and higher. 7.Tool (1) according to claim 5, characterized in that the matrix alloy iscomposed of austenitic manganese steel with a manganese concentration of6 to 25 wt. % Mn, preferably of 8 to 15 wt. % Mn.
 8. Method forproducing annular tools (1) having at least one working region (4)oriented radially outward and a clamping part (5) closer to the axis, inparticular roller bits or cutting rings for rock, in particular fortunnel boring machines, formed from an iron-based alloy as a matrix inwhich hard material particles, such as carbides and/or nitrides and/orcarbonitrides and/or borides, possibly in mixed form of the elementsfrom groups 4 and/or 5 of the periodic system, are incorporated,possibly for the production of a tool according to at least one of thepreceding claims, wherein a base alloy is melted and heated to atemperature of 1350° C. to 1630° C. in a first step and an addition or aformation of hard material particles with a higher density to or in themelt of the base alloy occurs in a second step, whereupon in a thirdstep, the matrix melt with the hard material particles is subjected to arotational motion about the longitudinal axis in a mold for the annulartool and is allowed to solidify.
 9. Method according to claim 8, whereinin a first step, a base alloy is melted with a chemical composition bywt. % of Carbon (C) up to 2.5 Silicon (Si) 0.01 to 3.0 Manganese (Mn)0.05 to 28.0 Chromium (Cr) up to 9.0 Nickel (Ni) up to 4.3 Molybdenum(Mo) up to 3.5 Tungsten (W) up to 2.2 (1.5×Mo+W) up to 5.1 Vanadium (V)up to 6.0 Niobium (Nb) up to 35.0 Aluminum (Al) up to 3.5, possiblyTitanium (Ti) up to 2.0 Zirconium (Zr) up to 3.0 Hafnium (Hf) up to 1.0Tantalum (Ta) up to 5.0 Cobalt (Co) up to 3.0 Iron (Fe) and impurityelements as the remainder.
 10. Method according to claim 8, wherein inthe second step, the hard material particles, such as carbides and/ornitrides and/or oxycarbonitrides and/or borides, possibly ascarbonitrides and/or oxycarbonitrides with boron components, at least ofone of the elements, or in mixed form of the elements, from groups 4 and5 of the periodic system, are introduced into the liquid base alloy bymeans of a solid or liquid metallic premelt or by means of a similarmixture of metal and hard material particles with a diameter of the hardparticles of less than 70 μm and homogeneously distributed in the basealloy, whereupon in the third step, a solidification of the mixture ofhard material particles and a matrix alloy, formed from the base alloyand the metal component of the premelt, occurs during rotational motionin the mold.
 11. Method according to claim 8, wherein the base alloywith a carbon content of under 0.6 wt. % C is melted and heated to atemperature of 1550° C. to 1630° C., whereupon in a second step, anaddition of the alloy elements carbon and/or nitrogen and/or boron,possibly as a pre-alloy, takes place and wherein these elements form,with the dispersed elements from group 4 and/or group 5 of the periodicsystem, primary carbides and/or nitrides and/or borides and/or compoundsor mixtures thereof in the melt, wherein the hard material particlesbeing formed have a total proportion of carbon, nitrogen and boron ofatomic ratios from 0.4 to 0.55 and a higher density than the melt, andthat 0.3 to 2.3 wt. % of carbon remains in the liquid metal, whereuponin a third step, the melt is subjected to a rotational motion about thelongitudinal axis in a mold for the annular tool and is allowed to cool,and a working and a heat treatment of the tool take place in additionalsteps.
 12. Method according to claim 11, wherein the elements fromgroups 4 and 5 of the periodic system are selected in terms of theirrespective concentration in the base alloy such that the density of theprimarily precipitated hard material particles is greater than that ofthe melt at a temperature 50° C. above the liquidus temperature.